Sea bed? (5)

I think it could be either:

Which length description are you looking for?:

berth

'sea bed?' is the definition.
(I've seen this in another clue)

This is all the clue.

(Other definitions for berth that I've seen before include "Bed on a ship/train" , "Bed for traveller" , "Bunk; mooring place" , "Bunk on ship or train" , "Place to sleep on a ship" .)

I've seen this clue in The New York Times and The Sun.

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